Photoluminescence (PL) is a process in which a substance absorbs photons and then re-radiates photons. Photoluminescent measurement is a contactless and non-destructive method of probing an electronic structure of materials.
Photoluminescence may be used to determine the quality of semiconductor material deposition on a substrate. For example, in thin-film photovoltaic device fabrication, semiconductor window and absorber layer materials are deposited over a substrate. Following deposition the substrate can then be irradiated by shining light into the substrate and measuring the photoluminescent spectrum which can indicate the quality of the semiconductor material depositions. After semiconductor deposition, photovoltaic devices are further fabricated in subsequent multiple steps. A measurement method and apparatus are needed which can detect deviations from desired processing conditions during such further fabrication of a photovoltaic device.